Travel Reference
In-Depth Information
to each island and the continent; but the vast physical changes that must have occurred dur-
ing the breaking up and subsidence of such extensive regions have led to the extinction of
some in one or more of the islands, and in some cases there seems also to have been time for
a change of species to have taken place. Birds and insects illustrate the same view, for every
family, and almost every genus of these groups found in any of the islands, occurs also on
the Asiatic continent, and in a great number of cases the species are exactly identical. Birds
offer us one of the best means of determining the law of distribution; for though at first sight
it would appear that the watery boundaries which keep out the land quadrupeds could be
easily passed over by birds, yet practically it is not so; for if we leave out the aquatic tribes
which are pre-eminently wanderers, it is found that the others (and especially the Passeres,
or true perching-birds, which form the vast majority) are generally as strictly limited by
straits and arms of the sea as are quadrupeds themselves. As an instance, among the islands
of which I am now speaking, it is a remarkable fact that Java possesses numerous birds
which never pass over to Sumatra, though they are separated by a strait only fifteen miles
wide, and with islands in mid-channel. Java, in fact, possesses more birds and insects pecu-
liar to itself than either Sumatra or Borneo, and this would indicate that it was earliest separ-
ated from the continent; next in organic individuality is Borneo, while Sumatra is so nearly
identical in all its animal forms with the peninsula of Malacca, that we may safely conclude
it to have been the most recently dismembered island.
The general result therefore at which we arrive is, that the great islands of Java, Sumatra,
and Borneo resemble in their natural productions the adjacent parts of the continent, almost
as much as such widely-separated districts could be expected to do even if they still formed
a part of Asia; and this close resemblance, joined with the fact of the wide extent of sea
which separates them being so uniformly and remarkably shallow, and lastly, the existence
of the extensive range of volcanoes in Sumatra and Java, which have poured out vast quant-
ities of subterranean matter and have built up extensive plateaux and lofty mountain ranges,
thus furnishing a
vera causa
for a parallel line of subsidence—all lead irresistibly to the
conclusion that at a very recent geological epoch the continent of Asia extended far beyond
its present limits in a south-easterly direction, including the islands of Java, Sumatra, and
Borneo, and probably reaching as far as the present 100-fathom line of soundings.
The Philippine Islands agree in many respects with Asia and the other islands, but present
some anomalies, which seem to indicate that they were separated at an earlier period, and
have since been subject to many revolutions in their physical geography.
Turning our attention now to the remaining portion of the Archipelago, we shall find that
all the islands from Celebes and Lombock eastward exhibit almost as close a resemblance to
